Many particulate materials are conveniently transported by truck, although they may also be transported by railcar, barge or by other means. Trucks that are used to transport such materials commonly include a tractor and an attached trailer having a tank or other container mounted thereon. Such trailers may also be loaded on railcars or barges, or a container may be mounted directly on a railcar or barge.
Frequently, these transport containers are referred to as pneumatic containers because of the pneumatic method, involving gas or air-entrainment, by which they may be loaded and unloaded. Particulate materials that are generally transported in pneumatic containers include agricultural products such as grain, corn kernels, beans, flour, sugar, peanuts and the like, light-weight aggregate products, and intermediate products for various industrial uses such as plastic pellets, powders, coke, lime, silica gel, powdered acid resins, rare earth powders, powdered alumina, and so forth.
Pneumatic containers generally include one or more product compartments that are usually cylindrical and/or spherical in shape in order to facilitate unloading by a method which involves pressurizing the compartments. Cylindrical or spherical product compartments are also generally easy to completely empty. For example, each product compartment may be provided with a discharge hopper that may be generally cylindrical or conical in shape. Each discharge hopper may have a material outlet at the bottom and a valve which controls the entry of material into the outlet.
An unloading system may also be provided which includes a blower or other mechanism for pressurizing air or another gas. The blower may provide the energy required for unloading the material from the container in the form of compressed air or another gas. For example, one end of a pressurizing gas conduit may be attached to the blower and the other end to a pressurizing gas inlet in the container. Operation of the blower compresses air or gas to move it through the pressurizing gas inlet into the container, thereby increasing the pressure of the air or gas above the material in the product compartments in the container in order to assist in discharging material through the hopper outlets. One end of a material conveying conduit may also attach to the blower and extend past and connect to each material outlet so that when the product compartment has been pressurized, air or another gas may be directed into the material conveying conduit to entrain material passing through each material outlet and carry it to the discharge end of the conduit. The container may be mounted on a frame which includes the undercarriage of a trailer. The product compartments of the container are generally enclosed by a sheet metal sheath, although the front of the sheath enclosure usually has a flat or nearly flat face.
It is known to streamline the undercarriage of a box-type trailer. However, the aerodynamic characteristics of a box-type trailer are quite different from those of a pneumatic container trailer.